The appearance in the circulation of lipopolysaccharide (LPS) is associated with sepsis and a greatly increased risk of neutrophil- mediated lung injury. The mechanisms by which neutrophils respond to LPS remain poorly understood, but the result is all too often sequestration in the pulmonary microcirculation and injury to the endothelium. We suggest here that these responses must eventually be understood in terms of the signalling cascades activated, and have focused on those resulting in activation of MAP kinases. Using both human and mouse systems, and a combined biochemical/genetic approach, our specific aims are: 1) To determine the signalling pathways used in response to LPS in the human and murine neutrophil, testing the hypothesis that LPS exposure will activate the tyrosine kinases Syk and Lyn leading to downstream activity of an MEKK, MKK3/6, and distinct p38 isoforms. 2) Determine the mechanisms by which p38 MAP kinases regulate translation of TNFalpha in neutrophils, with the hypothesis that specific p38 isoforms are essential in regulating translation of TNFalpha message by phosphorylating eIF-4E and increasing its affinity for the tranlsational complex. 3) To determine the mechanisms by which exposure of neutrophils to TNFalpha leads to activation of Jun-N- terminal kinases (JNKs), testing the hypothesis that exposure to TNFalpha in the context of integrin ligation leads to activation of Syk, Fgr, and Hck tyrosine kinases and downstream activation of MEKK1, MKK4, and JNK, which by phosphorylating c-Jun, allows induction of AP1- dependent genes, including MCP-1, to attract monocytes. 4) To determine the contribution of these pathways and feedback loops to neutrophil sequestration in the lung and subsequent injury. These studies will provide new information on the mechanisms by which the neutrophil responds to LPS with a complex repertoire of signalling cascades. Understanding this process may allow design of novel strategies for minimization of lung injury.